There is known a hybrid vehicle having an internal combustion engine and a motor/generator as a drive source and capable of operating in an electric vehicle (EV) mode in which a vehicle travels using power only from the motor/generator and in a hybrid electric vehicle (HEV) mode in which a vehicle travels using power from both the internal combustion engine and the motor/generator. As an example of a hybrid vehicle drive apparatus, JP2007-69817A discloses a configuration in which an internal combustion engine, a motor/generator, and a transmission are arranged in series, a first clutch is interposed between the internal combustion engine and the motor/generator, and a second clutch is interposed between the motor/generator and the transmission.
The control device for a hybrid vehicle discussed in JP2007-69817A releases the first clutch and engages the second clutch in the EV mode. In the HEV mode, the control device engages both the first and second clutches. Switching from the EV mode to the HEV mode is performed in a case where it is necessary to output power from the internal combustion engine when a user steps on an accelerator pedal during the EV mode, or in a case where a battery charge level is lowered.
For switching from the EV mode to the HEV mode, this control device causes the internal combustion engine to start through cranking by virtue of a drag torque of the first clutch while the second clutch slips. In this manner, by causing the second clutch to slip, the engagement of the first clutch progresses, and a torque change generated in the start of the internal combustion engine is prevented from being transferred to a drive wheel.